Margie's work for adding linear expressions is shown below. After checking her answer with the answer key, she solved it incorrectly.
Given (−3.78b + 12) − (4.82b − 16)
Step 1 −3.78b + 12 + (−4.82b) − 16
Step 2 −3.78b + (−4.82b) + 12 − 16
Step 3 (−3.78b + (−4.82b)) + (12 − 16)
Step 4 −8.6b + (−4)
Part A: Identify and explain the first step where Margie made an error. (2 points)
Part B: Explain how to correctly write the expression in fewest terms by correcting the error in Part A. Show all work. (2 points)